Value is determined by the scarcity of the merchandise; the more you have something to offer that no one else can provide, the more you’ll get paid.
When anyone asks me, “How do I figure out my value?” I say that value is the greatest amount that someone is willing to pay. It’s incredibly elastic, so it’s crucial that we continually put ourselves in a position to figure out how that value is shifting.
Great article by Whitney Hess on figuring out the difference between your value and your worth. Go check it out.